This invention relates to the delivery of lubricant to portions of a machine requiring lubrication and in particular to the measured flow of lubricant from a miniature positive displacement lubricant pump of the type that may be grouped into a lubrication system adapted to delivering metered volumetric quantity of lubricant separately to distinct portions of a machine.
An injection type of positive displacement metering pump is known in the art for providing reliable lubrication to individual portions of a machine, such as pneumatic cylinders, valves, bearings and the like. Such a pump is actuated by pulses of air and delivers a known volumetric quantity of lubricant for each actuating pulse. In this manner, the rate of lubricant delivery can be controlled by controlling the frequency of the actuating pulses. This direct relationship between frequency of actuation and rate of lubricant delivery will not be valid, however, if the supply of lubricant to the pump is interrupted, such as by an air pocket in the lubricant supply line, even minute air pockets in the lubricant may cause the amount of lubricant delivered by the pump to be less than the anticipated amount.
While slow measuring devices for pipe lines are known, such devices are relatively complex and typically provide either analog output signals or parallel digital output signals. Such analog and parallel digital signals require a significant amount of dedicated input circuitry for interface with a programmable controller. Because the input circuitry provided with a standard programmable controller is limited and typically is additionally assigned to the control of the machine being lubricated, the use of conventional flow measuring devices to individually monitor the volumetric quantities of lubricant flowing to numerous portions of a machine from individual positive displacement pumps would require an inordinately large amount of programmable controller input circuitry.